This invention relates to relatively narrow band antennas used with hand-held communications equipment. The invention is more specifically directed to such antennas which are disposed within the housing of the hand-held communications equipment.
Portable two-way radios have utilized a variety of antennas. One of the more common antennas used for such applications is a monopole. The use of a telescoping monopole is convenient since it can be retracted when not in use.
Antennas which are located within the housing of the portable communications equipment (subsequently referred to as an internal antenna) are desirable from the user's perspective. It eliminates a projecting external antenna which is subject to damage and may make a hand-held radio awkward to handle. Because of size limitations, internal antennas are often shorter than external antennas for the same frequency and have a narrower bandwidth.
When a conventional single input internal antenna is required to operate at two widely separated frequencies such as for separate transmit and receive frequencies, a matching circuit has been used in order to provide a reasonable impedance match at both frequencies. For example, U.S. Pat. No. 4,571,595 entitled DUAL BAND TRANSCEIVER ANTENNA (corresponding to Ser. No. 558,270) provides a matching circuit in order to cover two separated frequency bands.
A conventional two-way radio having separate transmit and receive frequencies utilizes a duplexer circuit which serves to simultaneously couple the transmitter output and the receiver input to a common antenna. The duplexer serves to isolate the transmitter and receiver from each other.